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Viewgraphs describe the Ames Research Center's cryogenics program. Diagrams are given of a fluid management system, a centrifugal pump, a flow meter, a liquid helium test facility, an extra-vehicular activity coupler concept, a dewar support with passive orbital disconnect, a pulse tube refrigerator, a dilution refrigerator, and an adiabatic demagnetization cooler.
Cooler technologies that are being developed by NASA to meet the varying temperature and cooling power requirements of NASA instruments are described. In addition to providing the desired operating temperature and cooling power by stabilizing temperatures from room temperature down to 0.1 K or less, these coolers will have working lifetimes commensurate with the 10 to 15 year lifetime expected for major future NASA facilities. The types of coolers currently under development are discussed, including radiative coolers, solid cryogen coolers, surface tension confined liquid cryogen coolers, mechanical coolers, liquid helium dewars, He3 adsorption coolers, adiabatic demagnetization refrigerators, and dilution refrigerators.
We describe the design, construction, and performance of an ultra-high vacuum (UHV) scanning tunneling microscope (STM) capable of imaging at dilution-refrigerator temperatures and equipped with a vector magnet. The primary objective of our design is to achieve a high level of modularity by partitioning the STM system into a set of easily separable, interchangeable components. This naturally segregates the UHV needs of STM instrumentation from the typically non-UHV construction of a dilution refrigerator, facilitating the usage of non-UHV materials while maintaining a fully bakeable UHV chamber that houses the STM. Here, the modular design also permits speedy removal of the microscope head from the rest of the system, allowing for repairs, modifications, and even replacement of the entire microscope head to be made at any time without warming the cryostat or compromising the vacuum. Without using cryogenic filters, we measured an electron temperature of 184 mK on a superconducting Al(100) single crystal.
Axion dark matter experiment ultra-low noise haloscope technology has enabled the successful completion of two science runs (1A and 1B) that looked for dark matter axions in the 2.66–3.1 μeV mass range with Dine–Fischler–Srednicki–Zhitnisky sensitivity. Therefore, it is the most sensitive axion search experiment to date in this mass range. Here, we discuss the technological advances made in the last several years to achieve this sensitivity, which includes the implementation of components, such as the state-of-the-art quantum-noise-limited amplifiers and a dilution refrigerator. Furthermore, we demonstrate the use of a frequency tunable microstrip superconducting quantum interference device amplifier in run 1A, and a Josephson parametric amplifier in run 1B, along with novel analysis tools that characterize the system noise temperature.
Superconducting quantum computers require microwave control lines running from room temperature to the mixing chamber of a dilution refrigerator. Adding more lines without preliminary thermal modeling to make predictions risks overwhelming the cooling power at each thermal stage. In this paper, we investigate the thermal load of SC-086/50-SCN-CN semi-rigid coaxial cable, which is commonly used for the control and readout lines of a superconducting quantum computer, as we increase the number of lines to a quantum processor. We investigate the makeup of the coaxial cables, verify the materials and dimensions, and experimentally measure the total thermal conductivity of a single cable as a function of the temperature from cryogenic to room temperature values. We also measure the cryogenic DC electrical resistance of the inner conductor as a function of temperature, allowing for the calculation of active thermal loads due to Ohmic heating. Fitting this data produces a numerical thermal conductivity function used to calculate the static heat loads due to thermal transfer within the wires resulting from a temperature gradient. The resistivity data is used to calculate active heat loads, and we use these fits in a cryogenic model of a superconducting quantum processor in a typical Bluefors XLD1000-SL dilution refrigerator, investigating how the thermal load increases with processor sizes ranging from 100 to 225 qubits. We conclude that the theoretical upper limit of the described architecture is approximately 200 qubits. However, including an engineering margin in the cooling power and the available space for microwave readout circuitry at the mixing chamber, the practical limit is approximately 140 qubits.
At FNAL two single cell 2.6 GHz SRF cavities are being used to search for dark photons, the experiment can be conducted at 2 K or in a dilution refrigerator. Precise frequency tuning is required for these two cavities so they can be matched in frequency. A cooling capacity constraint on the dilution refrigerator only allows piezo actuators to be part of the design of the 2.6 GHz cavity tuner. The tuner is equipped with three encapsulated piezos that deliver long and short-range frequency tuning. Modifications were implemented on the first tuner design due to the low forces on the piezos caused by the cavity. Three brass rods with Belleville washers were added to the design to increase the overall force on the piezos. The testing results at 2 K are presented with the original design tuner and with the modification.
There are several experiments ongoing at FNAL that require frequency tuning of bare (undressed) SRF cavities when they are cooled down and operated inside dilution refrigerator. One of these experiments is for the search of dark photons using a 2.6 GHz SRF cavity. The limited heat capacity of a dilution refrigerator prevents using a stepper motor for an SRF cavity tuner. The tuner for the 2.6 GHz SRF cavity will be equipped with encapsulated piezo actuators that will deliver long and short-range frequency tuning. Design of the tuner and results of the testing cavity/tuner system at ambient environment and at T = 77 K will be presented.
Neutron diffraction is a powerful tool in the study of quantum materials and associated emergent phenomena as it allows for direct detection of magnetic structure even at ultra-low temperatures. As pressure can drive systems across quantum critical points and tune emergent behaviors at the quantum scale, coupling neutron diffraction with extreme conditions of high pressure at (ultra-)low temperatures has been a key research target over decades. This has proven challenging as magnetic neutron diffraction typically requires large sample volumes due to flux limitations, whereas high-pressure studies require small sample volumes due to pressure limitations. Combining these two contradictory requirements poses many difficulties, but also brings opportunities in research and development. Here, we address these shortcomings through the use of a diamond anvil cell equipped with polycrystalline anvils with relatively large sample volumes coupled with the high neutron flux made available by the high-pressure diffractometer of the Spallation Neutron Source. This particular diamond anvil cell configuration has previously proven useful for single-crystal samples and is here coupled with the ultra-low temperatures of a dilution refrigerator for the first time. Our study on a single crystal of Yb 2 O 3 successfully collected magnetic neutron diffraction data at 5.3 GPa below 200 mK inside a dilution refrigerator. We have performed a detailed analysis of the magnetic diffraction data to investigate the magnetic structure under pressure and observed a subtle shift in the transition temperature. This development will open the door for future studies on magnetic materials with these much-desired coupled extremes of high pressure and ultra-low temperatures.
A number of future space missions require liquid helium for cooling scientific payloads. These missions will require the long term storage and resupply of liquid helium at temperatures of 1.4 - 2.1 Kelvin. In addition, some of the proposed instruments will require refrigeration to temperatures as low as 50 mK. A variety of liquid helium based refrigerator systems could provide this subkelvin cooling. The status of helium storage and refrigeration technologies and of several alternative technologies is presented here along with areas where further research and development are needed. (Helium resupply technologies are the topic of another presentation at this symposium). The technologies covered include passive and dynamic liquid helium storage, alternatives to liquid helium storage, He -3 refrigerators, He -3/He -4 dilution refrigerators, and alternative sub-kelvin coolers.
The book presents a review of literature on superfluid helium, together with papers under the topics on heat and mass transfer in He II; applications of He II for cooling superconducting devices in space; heat transfer to liquid helium and liquid nitrogen; multilayer insulation; applications of superconductivity, including topics on magnets and other devices, magnet stability and coil protection, and cryogenic techniques; and refrigeration for electronics. Other topics discussed include refrigeration of superconducting systems; the expanders, cold compressors, and pumps for liquid helium; dilution refrigerators; magnetic refrigerators; pulse tube refrigerators; cryocoolers for space applications; properties of cryogenic fluids; cryogenic instrumentation; hyperconducting devices (cryogenic magnets); cryogenic applications in space science and technology and in transportation; and miscellaneous cryogenic techniques and applications.
Prototype dilution cryocoolers based on dilution refrigeration and adiabatic demagnetization refrigeration (ADR) cycles were designed, constructed, and tested. Although devices the devices did not operate as fully functional dilution cryocoolers, important information was gathered. The porous metal phase separator was demonstrated to operate in the -1-g configuration; this phase separation is the critical element in the He-3 circulation dilution cryocooler. Improvements in instrumentation needed for additional tests and development were identified.
Several disciplines requiring in-space cryogenic cooling are identified including high-energy, gamma-ray, and IR astronomy, relativity missions, and superconducting devices. Radiant coolers are limited in terms of temperature ranges and cooling loads. Other spacecraft cryogenic systems include stored solid cryogenic coolers using materials such as hydrogen, neon, argon, and methane. Two such cooler designs are described including one for the Nimbus F limb radiance inversion radiometer and one for the Nimbus G limb infrared monitoring of the atmosphere. Suggestions for increasing the performance of solid cryogenic coolers are made, such as a multimission cooler, a mechanical refrigerator, Stirling-cycle refrigerators, and Vuilleumier mechanized coolers. Techniques for obtaining cryogenic cooling in the milli-K range are identified as dilution refrigeration and adiabatic demagnetization.
Several techniques were surveyed for the refrigeration, reliquefaction and production of slush from hydrogen. The techniques included auger; bubbling helium gas; Simon desorption; the Petlier effect; Joule-Kelvin expansion using Stirling, Brayton, and Viulleumirer approaches; rotary reciprocating; a dilution refrigerator; adiabatic demagnetization of a paramagnetic salt; and adiabatic magnetization of a superconductor.
We propose cyclic refrigeration in solid state, employing a gas of magnetic field vortices in a type-II superconductor—also known as fluxons—as the cooling agent. Refrigeration cycles are realized by envisioning a racetrack geometry consisting of both adiabatic and isothermal arms, etched into a type-II superconductor. The guided propagation of fluxons in the racetrack is achieved by applying an external electrical current, in a Corbino geometry, through the sample. A gradient of magnetic field is set across the racetrack allowing one to adiabatically cool down and heat up the fluxons, which subsequently exchange heat with the cold and hot reservoirs, respectively. We characterize the steady state of refrigeration cycles thermodynamically for both s -wave and d -wave pairing symmetries, and present their figures of merit such as the cooling power delivered, and the coefficient of performance. Our cooling principle can offer significant cooling for on-chip microrefrigeration purposes, by locally cooling below the base temperatures achievable in a conventional dilution refrigerator. We estimate n W / m m 2 of cooling power per unit area assuming a tunnel coupling with ∼ M Ω µ m 2 specific resistance. Integrating the fluxon fridge to quantum circuits can enhance their coherence time by locally suppressing thermal fluctuations, and improve the efficiency of single photon detectors and charge sensors. Published by the American Physical Society 2024
The development of a continuous adiabatic demagnetization refrigerator (CADR) has progressed to the point where we have demonstrated a 4-stage system that provides continuous cooling at 50 mK and below, while rejecting heat to a 4.2 K helium bath. Since temperature control and cycling of the ADR is fully automated, the system is simple to operate and stable. Temperature fluctuations of the cold tip are typically less than 10 microKelvin rms (at 100 mK). The ADR s cooling power of 2 1 microwatts at 100 mK is comparable to that of small dilution refrigerators, but because its efficiency is so much higher (50% of Carnot), the peak heat rejection rate is less than 10 mW. This is significant in allowing the ADR to be cooled by relatively low-power cryocoolers. In addition to commercial pulse-tube and Gifford McMahon (GM) coolers, this potentially includes small GM systems that run on 120 V power and do not need water cooling. The present focus is to design and fabricate a small dewar to house the CADR and a cryocooler, in anticipation of making a cryogen-free, low cost CADR commercially available. Performance of the prototype CADR and the complete system will be discussed.
Future large-scale quantum processors (i.e. 100s of qubits), especially those based on superconducting circuits, will require large cooling powers (~10s of microW) at very low temperatures (<50 mK) with stringent temperature stabilities to avoid quantum decoherence and thus guarantee successful operation of such systems. One attractive option for providing this cooling is through Continuous Adiabatic Demagnetization Refrigerators (CADR). Scalable state-of-the-art CADRs at NASA's Goddard Space Flight Center have successfully shown to lift 6 W of heat at 50 mK with a 1 K temperature stability while rejecting its heat to a cryocooler at 4K. Carefully planned and proper heat sinking of cables, attenuators, and microwave components at various temperature stages (between 4K and base temperature) is critical in the cooling architecture of quantum computers and can be provided through proper staging of each unit within the CADR system. As an alternative method of cooling, dilution refrigerators with the potential to meet cooling requirements of emerging large-scale quantum processors are also discussed.
Magneto-optical sensors including spin noise spectroscopies and magneto-optical Kerr effect microscopies are now ubiquitous tools for materials characterization that can provide new understanding of spin dynamics, hyperfine interactions, spin-orbit interactions, and charge-carrier g-factors. Both interferometric and intensity-difference measurements can provide photon-shot-noise-limited sensitivity, but further improvements in sensitivity with classical resources require either increased laser power that can induce unwanted heating and electronic perturbations or increased measurement times that can obscure out-of-equilibrium dynamics and slow experimental throughput. Proof-of-principle measurements have already demonstrated quantum enhanced spin noise measurements with a squeezed readout field that are likely to be critical to the nonperturbative characterization of spin excitations in quantum materials that emerge at low temperatures. Here, a truncated nonlinear interferometric readout for low-temperature magneto-optical Kerr effect and related magneto-optical microscopies that is accessible with today's quantum optical resources is proposed. 10 nrad/$\sqrt{Hz}$ sensitivity is achievable with optical power as small as 1 µW. As a result, measurements may be performed at temperatures as low as 83 mK in commercially available dilution refrigerators. This combination of high sensitivity and low operating temperature is impossible to achieve with any classical measurement. The quantum advantage for the proposed measurements persists even in the limit of large loss and small squeezing parameters.
The Simons Observatory is building both large (6 m) and small (0.5 m) aperture telescopes in the Atacama Desert in Chile to observe the cosmic microwave background CMB radiation with unprecedented sensitivity. Simons Observatory telescopes in total will use over 60,000 transition edge sensor (TES) detectors spanning center frequencies between 27 and 285 GHz and operating near 100 mK. TES devices have been fabricated for the Simons Observatory by NIST, Berkeley, and HYPRES/SeeQC corporation. Iterations of these devices have been tested cryogenically in order to inform the fabrication of further devices, which will culminate in the final TES designs to be deployed in the field. The detailed design specifications have been independently iterated at each fabrication facility for particular detector frequencies. We present test results for prototype devices, with emphasis on NIST high frequency detectors. A dilution refrigerator was used to achieve the required temperatures. Measurements were taken both with 4-lead resistance measurements and with a time-domain Superconducting Quantum Interference Device (SQUID) multiplexer system. The SQUID readout measurements include analysis of current versus voltage (IV) curves at various temperatures, square wave bias step measurements, and detector noise measurements. Lastly, normal resistance, superconducting critical temperature, saturation power, thermal and natural time constants, and thermal properties of the devices are extracted from these measurements.